TV tech terms demystified, part 3: Color standards, definitions
In this, the third installment in our series that cuts through the BS that is routinely used to market new televisions, we define the terms, standards, and specs involving color. In case you missed the first two installments, you can use either the navigation tools above and at the end of the story, or you can go directly to our discussion of screen size, resolution, and refresh speed, and our explanations of display types and technologies.
Adobe RGB: A color standard/space implemented to roughly match the spectrum attained by the paper and ink world’s CMYK (Cyan, Magenta, Yellow, and blacK). TV vendors will use Adobe RGB as a point of comparison, which is fine for HDTV; but for Ultra HD (popularly—if not entirely accurately—described as 4K), look for comparisons to Rec.2020. Adobe RGB covers more colors than sRGB, but fewer than Rec.2020.
Color depth (aka bit depth): The number of bits in a digital video signal that are used for each color component of a single pixel. With 8-bit color, there are three bits for the red component, three bits for green, and two bits for blue (3:3:2). Why only two bits for blue Because the human eye is less sensitive to the blue component of color. (See also: Deep Color and True Color, below.)
Color space: The range—or gamut—of colors a video display can produce. There are various color-space standards, but the ones most commonly associated with TVs are—from narrowest to broadest—are sRGB, from Rec. 709 (from the HDTV spec); Adobe RGB; and Rec. 2020 (from the Ultra HD spec). Vendors will say their TV meets N percentage of X space.
Deep Color: 30-, 36-, or 48-bit color depth. A digital video signal supporting Deep Color uses 10-, 12- or 16 bits for each of the red, green, and blue components of a pixel to deliver billions of colors. The HDMI spec supports Deep Color starting with HDMI 1.3. (See also: Color depth, above.)
High Dynamic Range (HDR): This simply means lighter lights, darker darks (by comparison) and, as a result, more range in between. In today’s TV market, HDR is more a result than a standard for accomplishing it. You’ll see it labeled X-Tended Dynamic range (Sony), Ultra Luminance (LG), or even the ostentatious Peak Illuminator Ultimate (Samsung). Vizio simply uses Dolby’s Dolby Vision. Only Panasonic calls it HDR. It’s generally accomplished by making the screen brighter, e.g. 800- versus the 400 nits that’s common in the current generation of TVs. You’ll find a deeper exploration of high-dynamic-range TVs here. (Note: Don’t confuse this definition of HDR with the HDR used in photography, where different levels of exposure are combined to produce an image with a wider range of brightness and contrast.)
HSL (Hue/Saturation/Luminance): Another way to refer to and adjust colors. Put simply: hue is the color, saturation is the amount of said color, and luminance (or brightness) is how bright or dark it is. You’ll also run into HSL in some TV color-calibration dialog boxes.
RGB (Red/Green/Blue): The three colors of pixels that most displays use in trios to form the other colors in the spectrum. This is done by varying the individual intensity or luminance of each dot in the trio. You may be familiar if you’ve adjusted a TV that uses the reference, or created a custom color on your computer where you’ll have 256 levels (0-255) each of red, green, and blue.
Rec. 2020: An abbreviation of ITU-R Recommendation BT.2020, where ITU is the International Telecommunications Union. While Rec.2020 also deals with resolution and frame rates, in terms of color, it is the current definition/target for the spectrum that an Ultra HD (or higher resolution) cinematic display should reproduce. When you hear someone say their TV reaches 98 percent of Rec. 2020, they mean the TV can reproduce 98 percent of the colors in that standard.
Rec. 709: The resolutions, frame rates, and other specs for HDTV that encompass the sRGB color space (see below).
sRGB: The original color space for computers and color displays and matched by Rec. 709 (HDTV). Slightly smaller than the Adobe RGB color space and considerably smaller than Rec. 2020.
True Color: 24-bit color depth. A digital video signal supporting True Color uses 8 bits for each of the red, green, and blue components of a pixel to produce 16,777,216 colors. (See also: color depth.)